Conventionally, in order to measure a cornea shape with precision, a cornea shape measuring apparatus for projecting an index, for example, a Placido's pattern to the cornea of an eye to be examined has been known.
Note that “cornea shape measurement” in this specification includes not only cornea mapping measurement for a central cornea shape of a cornea central region, a peripheral cornea shape of a cornea peripheral region, or the like but also measurement for, for example, a corneal curvature radius, a corneal astigmatic, or a corneal astigmatic axial angle.
On the other hand, an eye refractive power measuring apparatus which is called a so-called refractometer has been known as an apparatus for measuring eye refractive power of an eye to be examined.
In general, data and the like related to a cornea shape and eye refractive power are important data for conducting suitable diagnosis, and it is desirable that these data are obtained by measurement using a single apparatus. In addition, there is a demand to reduce an occupying space of an apparatus. In view of such requirements, in recent years, an ophthalmologic apparatus of a type having a complex function which is provided with both a function for measuring a cornea shape and a function for measuring eye refractive power, which are described above, also makes its appearance.
According to such an ophthalmologic apparatus, a circular hole portion is formed in a central region of a Placido's plate for forming, for example, a Placido's pattern, and then an index light flux for eye refractive power measurement is projected through the hole portion and reflected light from an eye fundus is received through the hole portion so that cornea shape data and eye refractive power data can be obtained by a single apparatus.
Now, when a cornea shape is analyzed, it is desirable that a measurement area of the cornea shape can be made to extend to the vicinity of a cornea central portion. For example, it is desirable that a ring pattern of Φ 1.0 is projected onto a cornea and cornea shape measurement based on the ring pattern is conducted. Therefore, it is considered that a smallest ring on the above-mentioned Placido's plate is further made smaller to make the hole portion small.
However, when the hole portion is made to a predetermined size or smaller, projection and receipt of a light flux for eye refractive power measurement are inhibited. Thus, when a measurement area of a cornea shape measuring apparatus is increased, there is a possibility that a reduction in measurement sensitivity of eye refractive power is caused and an erroneous measurement result is calculated so that misdiagnosis of an examiner is induced.
As described above, there is a limitation with respect to the measurement area of the cornea shape so that the vicinity of the cornea central region cannot be measured.
The present invention has been made in view of the above circumstances, and an object thereof is to provide an ophthalmologic apparatus which can measure a cornea shape in the vicinity of a cornea central region without blocking a light flux for measuring eye refractive power and accurately measure the eye refractive power.